1. Field of the Invention
This invention has relation to safety locks for knob-operated doors wherein a loop attached to a door frame is positioned over a doorknob to prevent the door from being fully opened.
2. Description of the Prior Art
It is well known to fasten loops or rings of cable or chain or the like to door frames in position so that they can be slid over doorknobs to prevent doors from being opened more than part way.
U.S. Pat. No. 878,607 granted to Cairns in February of 1908 shows a chain with a loop in it fastened to the door frame with the loop slipped over a doorknob.
U.S. Pat. No. 2,726,112 granted to Conhagen in December of 1955 shows a double loop of chain which can be hung over the doorknob to hold the door in a partly closed condition.
U.S. Pat. No. 3,451,708 granted to Brooks in June of 1969 shows a continuous ring on the end of a chain mounted so that the ring can be slid over the doorknob to hold the door from opening.
U.S. Pat. No. 3,640,558 granted to Gewertz et al in February of 1972 shows the concept of chain loops hung over doorknobs similar to the showing of the patent to Conhagen.
U.S. Pat. No. 3,804,454 granted to Simmons in April of 1974 shows a safety doorguard made up of first and second loops of cables separated by a collar which firmly holds the cable loops. The second cable loop is fastened to a door frame by a fastener which encircles the second loop and is slidable with respect to it. The first loop is in position to slide over the doorknob of a door adjacent the door frame. As seen in FIG. 6 of that patent, the loop is designed to fit loose enough so that the door can be opened far enough for the occupant inside to see the identity of the person at the door. This leaves the cable loops and the collar vulnerable to cutting action by a person outside the door if the door is opened surreptitiously by such person with forced entry as an object.
The above patents were the closest found on a search of the present invention. The inventor and those in privity with him are aware of no prior art closer than that set out above and are aware of no prior art which anticipates the claims herein.